This invention relates to planetary gearing and more particularly to planetary gearing for use with a traction type continuously variable transmission.
Continuously variable transmissions (CVT) incorporate a continuously variable unit (CVU) and planetary gearing to provide a substantially continuously variable ratio between an engine and the drive wheels of a vehicle. The CVU can be of the belt type or the traction type commonly called a toric drive. The belt type requires the input shaft and the output shaft of the CVU to be on non-coaxial spaced axis. The traction type permits the input and output shaft to be located coaxially. This arrangement lends itself to rear wheel drive vehicles where the barrel diameter of the transmission is an important design consideration.
Many prior art arrangements of traction drive CVTs include a transfer shaft between the planetary gearing and the CVU to connect the CVU output with a member of a summing gear set that also has a member connected with the CVU input. These arrangements, of course, increase the barrel diameter of the transmission housing. One prior art arrangement shown in U.S. Pat. No. 5,607,372 discloses a CVT having a centrally disposed planetary carrier and two sun gears meshingly interconnected to permit coaxial input and output members of the CVU. This arrangement does add axial length to the transmission package.
It is an object of the present invention to provide an improved gearing arrangement for a geared neutral continuously variable transmission (CVT).
In one aspect of the present invention, a continuously variable unit (CVU) is operatively connected with a gearing arrangement comprised of three planetary gear sets and two torque transmitting mechanisms. In another aspect of the present invention one of the planetary gear sets is a compound planetary gear set and the other two are simple planetary gear sets. In yet another aspect of the present invention, the compound planetary gear set is disposed adjacent the CVU and the two simple planetary gear sets are disposed between the compound planetary gear set and the output of the CVT.
In still another aspect of the present invention, the sun gears of each of the planetary gear sets each have only a single rotating shaft passing concentrically therethrough. In a further aspect of the present invention, the ring gear member of the compound planetary gear set and the carrier assembly member of one of the simple planetary gear sets are connected with a rotatable shaft that pass concentrically through both sun gear members of the simple planetary gear sets. In a yet further aspect of the present invention, the carrier assembly member of the compound planetary gear set is drivingly connected with an input shaft of the CVU which passes concentrically through the sun gear member of the compound planetary gear set. In a still further aspect of the present invention, the torque transmitting mechanisms are disposed in a location that permit the supply of pressurized fluid thereto through a single support member located at one end of the transmission housing.
The transmission is comprised of a continuously variable unit of the traction type. The CVU has two input discs or shells and two output discs or shells. The input and output discs are frictionally interconnected in pairs by traction members. The output discs are driven rotationally through the traction members by the input discs that are driven by a prime mover such as an engine. The input disc and the output discs are also interconnected through a compound planetary gear set that serves to combine the rotary motion of both for delivery to a pair of simple planetary gear sets. The input discs are drivingly connected with the carrier assembly member of the compound planetary gear set by a shaft that passes concentrically through and rotatably supports the sun gear member which is drivingly connected with the output discs.
The two simple planetary gear sets have interconnected sun gear members that are rotatably supported on a shaft drivingly connected between the carrier assembly member of one simple planetary gear set and a first selectively engageable friction torque transmitting mechanism. The one carrier assembly member is also drivingly connected with the ring gear member of the compound gear set. The carrier assembly member of the other simple planetary gear set is operatively connected with a second selectively engageable friction torque transmitting mechanism and the ring gear member is connected with an output shaft and the first torque transmitting mechanism.
In one embodiment of the invention, the ring gear member of the compound planetary gear set and the carrier assembly member of the one simple planetary gear set are interconnected by a hub or shell that surrounds the one simple planetary gear set. The carrier assembly member of the compound planetary gear set and the ring gear member of the one simple planetary gear set are interconnected by a hub disposed between the planetary gear sets.
In another embodiment of the invention, the carrier assembly member of the compound planetary gear set and the ring gear member of the one simple planetary gear set are drivingly interconnected by a hub or shell that surrounds the exterior and partially encloses one end of the compound planetary gear set. The ring gear member of the compound planetary gear set and the carrier assembly member of the one simple planetary gear set are drivingly interconnected by a hub disposed between the planetary gear sets.
In both embodiments of the present invention the torque transmitting mechanism disposed between the carrier assembly member of the one simple planetary gear set and the ring gear member of the other simple planetary gear set is selectively engaged to provide a low range output. The torque transmitting mechanism connected with the carrier assembly member of the other simple planetary gear set is selectively engaged to provide a high range output. Also both embodiments are radially compact since the sun gear members of each planetary gear set only has to accommodate one rotating shaft disposed concentric therewith. As those familiar with the art will appreciate, a small sun gear member diameter permits a smaller overall radial dimension for the planetary gear set.